My wife 98 discovery leaks coolant from the coolant reservoir cap and then overheats. When the truck gets to normal operating temp, it starts to boil the coolant and it comes out the cap as steam and coolant. Then the temp starts to raise. If she turns the heater on the truck it sometimes help with the heating problem. Any help with this issue is greatly appreciated.

Thanks.

 

I would stop driving it immediately until you find out what exactly's going on.

How old is the thermostat?

Do you have white smoke coming out the exhaust? Any check engine lights? Is the oil milky or smell like coolant?

 

Thermostat is about 5yrs. No white smoke at all and no check engine light as of yet.

 

possible thermostat but possible issue with cracked heads or engine.

put some dye in the coolant system and check to see where there are leaks including the spark plugs.

 

10-1 odds it's your thermostat, since what you describe are the typical stuck thermostat symptoms. Cheap $8 fix if that's the case. Changing the thermostat is extremely simple. On the passenger side of the vehicle, your radiator hoses connects the thermostat housing which looks like this:

Remove the radiator hose from the housing, then remove the 2 retaining bolts and lift up the housing. The thermostat will either just be sitting there, or stuck to the housing itself with goop hanging from it. Replacement is as simple as cleaning the housing, and sitting the new thermostat and gasket in the hole, tighten the bolts and replace the radiator hose. 20 minutes your first time. Your wife can do it if you prefer!

 

yeah.... you should change the thermostat asap.. and also check out mikes 60k service sticky in the HOW TO section.. sounds like the truck could use some loving.

 

Do not let these trucks overheat too many times or you be replacing your engine. If your coolant is boiling that means that it is not holding pressure so there is a leak and sounds like you need a new expansion tank cap. You can try a new thermostat but they generally fail open not closed, put it in boiling water and test it see if it opens and closes.

 

Hey im dealing with the same problem(2000 disco ii)... Just changed the t stat/housing and no go!... Still boils over out of expansion tank and starts to over heat!

 

Replace your expansion tank cap

 

Have you checked your water pump?